A photoplethysmogram (PPG) signal can be measured by PPG systems to derive corresponding physiological signals (e.g., pulse rate). In a basic form, PPG systems can employ a light source or light emitter that emits light through an aperture into the user's tissue. In addition, a light detector can be included to receive light through an aperture that reflects off and exits the tissue. However, determination of the user's physiological signals can be erroneous due to variations in the user's skin type, usage conditions, and environmental conditions affecting the signal of the reflected light.
For a given light emitter and light detector, the PPG signal can decrease as the separation distance between the light emitter and light detector increases. On the other hand, perfusion index can increase as the separation distance between the light emitter and light detector increases. Therefore, shorter separation distances between a light emitter and a light sensor can favor high PPG signal strength, while longer separation distances can favor high perfusion index values (e.g., motion performance). Additionally, the size of the light emitter and/or light detector apertures can lead to insufficient PPG signal strength and/or excessive ambient light intrusion that can introduce noise into the signal and can saturate the signal. Both insufficient PPG signal strength and excessive ambient light intrusion can lead to erroneous measurements. Furthermore, the location or shape (or both) of the apertures may not account for variations in the user's skin that can negatively impact the measurements. While certain architectures, such as multiple path length architectures, can be employed to alleviate these issues, the path lengths and aperture sizes, locations, or shapes cannot be adjusted once the device is manufactured. To account for different skin types, usage conditions, and environmental conditions, a device with dynamically reconfigurable apertures may be needed.